1. Field of Invention
The present invention relates to a method for recognising the type of fuel actually used in an internal combustion engine.
2. Description of Related Art
For many years, internal combustion engines with controlled ignition have been fed with different types of liquid fuel, such as pure petrol, hydrated alcohol, or a mixture of petrol and alcohol. Importantly, these different types of liquid fuels each have different characteristics, such as different stoichiometric air/fuel ratios. Recently, even modern diesel engines can be fed with fuels other than pure diesel which consist of a mixture of diesel and fuels from bio-mass, such as vegetable oils like rapeseed oil (commercially known as “biodiesel”).
Accordingly, it is important for the electronic control unit of the engine to know the type of fuel that is actually used by the internal combustion engine so as to optimise the combustion control as a function of the features of the fuel actually used. For example, it is essential to know the actual stoichiometric air/fuel ratio of the fuel in order to minimise the generation of pollutants. Further, it is very useful to know the volatility of the fuel to ensure a proper “cold” start of the internal combustion engine.
Several methods for recognising the type of fuel are known in the art which are based on information provided by a lambda probe in the exhaust. However, there is a need in the art to be able to recognise the type of fuel without the use of information provided by the lambda probe in the exhaust. Specifically, it is important to be able to recognise the type of fuel when in “recovery” mode (when the lambda probe is not working properly). Further, it is desirable to increase the recognition reliability by comparing the recognition of the type of fuel provided by the lambda probe with another independent recognition source.
The published Italian patent application BO2011A000122 (corresponding to published U.S. patent application US2013067990) describes a method for recognising the type of fuel actually used in an internal combustion engine, comprising the steps of: sensing the intensity of vibrations generated by the internal combustion engine in a measurement time window; determining the value of a synthetic index by processing the intensity of the vibrations generated by the internal combustion engine in the measurement time window; comparing the synthetic index with a predetermined comparison quantity; and recognising the type of fuel as a function of the comparison of the synthetic index to the comparison quantity.
The recognition method described in published Italian patent application BO2011A000122 allows the type of fuel actually used by the internal combustion engine to be estimated with a high enough accuracy and reliability. In addition, this recognition method is completely independent of the information provided by the lambda probe in the exhaust of the internal combustion engine. However, when using the recognition method described in published Italian patent application BO2011A000122, it is possible that the recognition of the type of fuel actually used by the internal combustion engine is relatively uncertain (i.e. not completely reliable). The published U.S. patent application US2012031374 describes a method for recognising the type of fuel actually used in an internal combustion engine as a function of a detonation value measured with a detonation sensor.